Proposed resolution (approved by CWG 2022-08-26):

Add a new paragraph after 9.7.1 [dcl.enum] paragraph 8:

For an enumeration whose underlying type is fixed, ...

An enumeration has the same size, value representation, and alignment requirements (6.7.3 [basic.align]) as its underlying type. Furthermore, each value of an enumeration has the same representation as the corresponding value of the underlying type.

Two enumeration types are layout-compatible enumerations if ...

Suggested resolution [SUPERSEDED]:

Add a new paragraph after 9.7.1 [dcl.enum] paragraph 8:

For an enumeration whose underlying type is fixed, ...

An enumeration has the same size, value representation, and alignment requirements (6.7.3 [basic.align]) as its underlying type. Furthermore, each value of an enumeration has the same representation as the same value of the underlying type.

Two enumeration types are layout-compatible enumerations if ...

[Accepted as a DR at the November, 2022 meeting.]

Subclause 9.7.1 [dcl.enum] specifies how the underlying type of an enumeration is determined, and, for enumerations whose underlying type is fixed, specifies that the enumeration has the same set of values as the underlying type. However, the specification does not relate the size and alignment requirements of the enumeration to those of the underlying type. Those ought to be the same.